How to do?: Stack of limited size containing unique items.

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mark4asp - 28 Sep 2007 15:29 GMT

Stack of limited size containing unique items?

Hi guys,

How would I implement a stack of limited size containing unique items?

For example. Suppose my stack has [3,5]. I add 2 to it and it is now
[3,5,2]. Now I want to add 5 to the unique item stack so it should
now be: [3,2,5]. The item added is pulled from the stack, then pushed.
The stack should also have a maximum size of 4 items. I add 4 and 7
respectively. It becomes: [3,2,5,4] then, after adding 7: [2,5,4,7].
The first item is dropped when the stack is at maximum capacity and a
new item added. Should this be a queue rather than a stack? I said
'stack' because, apart from the limited size behavior of the oldest
item being dropped in favour of the new item, I want it to have the
FILO behavior of a conventional stack.

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Göran Andersson - 28 Sep 2007 16:01 GMT

> Stack of limited size containing unique items?
>
[quoted text clipped - 12 lines]
> item being dropped in favour of the new item, I want it to have the
> FILO behavior of a conventional stack.

Neither a Stack<> or a Queue<> has any method for removing an item in
the middle of the collection, so they aren't really useful in this case.

I would suggest that you use a List<> or array as internal storage in a
class, and just implement the methods you need. The List<> class has the
methods Contains and RemoveAt that might be useful, but as your
collection has a fixed maximum size, using an array might feel like a
more straight forward solution.

Signature

Göran Andersson
_____
http://www.guffa.com

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mark4asp - 28 Sep 2007 16:07 GMT

> Stack of limited size containing unique items?
>
[quoted text clipped - 12 lines]
> item being dropped in favour of the new item, I want it to have the
> FILO behavior of a conventional stack.

OK, figured it.

using System;
using System.Collections.Generic;

public class StackLimited
{
    int _maxSize;
    List<int> _stack;
    public StackLimited(int maxSize)
    {
        _maxSize = maxSize;
        _stack = new List<int>(maxSize);
    }
    public void Push(int item)
    {
        if(_stack.Contains(item))
            _stack.Remove(item);
        else
            if (_stack.Count == maxSize)
            {
                Pop();
            }
        _stack.Insert(0, item);
    }
    public int Pop()
    {
        if (_stack.Count > 0)
        {
            data = _stack[0];
            _stack.RemoveAt(0);
        }
    }
}

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Göran Andersson - 28 Sep 2007 16:30 GMT

>> Stack of limited size containing unique items?
>>
[quoted text clipped - 35 lines]
> {
> Pop();

But that will remove the most recent item, not the oldest one.

>             }
>         _stack.Insert(0, item);
[quoted text clipped - 8 lines]
>     }
> }

Signature

Göran Andersson
_____
http://www.guffa.com

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How to do?: Stack of limited size containing unique items.

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